Field of the Disclosure
This disclosure relates to a component for turbochargers for internal combustion engines. More particularly, this disclosure relates to a tapered-land thrust bearing assembly with inserts (such as ramps or pads) for varying effective geometry to increase the bearing's optimal operating range.
Description of Related Art
Advantages of turbocharging include increased power output, lower fuel consumption and reduced pollutant emissions. The turbocharging of engines is no longer primarily seen from a high power performance perspective, but is rather viewed as a means of reducing fuel consumption and environmental pollution on account of lower carbon dioxide (CO2) emissions. Currently, a primary reason for turbocharging is using the exhaust gas energy to reduce fuel consumption and emissions. In turbocharged engines, the combustion air is pre-compressed before being supplied to the engine. The engine aspirates the same volume of air-fuel mixture as a naturally aspirated engine, but due to the higher pressure, thus higher density, more air and fuel mass is supplied into the combustion chamber. Consequently, more fuel can be burned, so that the engine's power output increases relative to the speed and swept volume.
In exhaust gas turbocharging, some of the exhaust gas energy, which would normally be wasted, is used to drive a turbine. The turbocharger returns some of this normally wasted exhaust energy back into the engine, contributing to the engine's efficiency and saving fuel. A compressor, which is mounted on the same shaft as the turbine, draws in filtered ambient air, compresses it, and then supplies it to the engine.
A turbocharger is a type of forced induction system used with internal combustion engines. Turbochargers deliver compressed air to an engine intake, allowing more fuel to be combusted, thus boosting an engine's horsepower without significantly increasing engine weight. Thus, turbochargers permit the use of smaller engines that develop the same amount of horsepower as larger, naturally aspirated engines. Using a smaller engine in a vehicle has the desired effect of decreasing the mass of the vehicle and enhancing fuel economy. Moreover, the use of turbochargers permits more complete combustion of the fuel delivered to the engine, which contributes to the highly desirable goal of a cleaner environment.
Turbochargers typically include a turbine housing connected to the engine's exhaust manifold, a compressor housing connected to the engine's intake manifold, and a center bearing housing coupling the turbine and compressor housings together. A turbine wheel in the turbine housing is rotatably driven by an inflow of exhaust gas supplied from the exhaust manifold. A shaft rotatably supported in the center bearing housing connects the turbine wheel to a compressor impeller in the compressor housing so that rotation of the turbine wheel causes rotation of the compressor impeller. The shaft connecting the turbine wheel and the compressor impeller defines an axis of rotation. As the compressor impeller rotates, it increases the air mass flow rate, airflow density and air pressure delivered to the engine's cylinders via the engine's intake manifold.
Friction minimizing systems are common in the design of turbochargers due to their high rotating speed. With a sleeve bearing, the shaft turns on an oil film on a bushing or the like. For the turbocharger, the oil supply may come from the engine oil circuit. Floating bushings, rotating slower than shaft speed, can be situated between the stationary center bearing housing and the rotating shaft to reduce friction.
Thrust bearings support axial loads from the rotating impellers/wheels. Regarding forces in an axial direction, as the forces acting on the compressor and turbine wheels in an axial direction are of differing magnitude, the shaft and turbine wheel assembly is displaced in an axial direction.
The axial thrust bearing supports these forces. Small discs or rings fixed on the shaft may serve as running surfaces with an oil film in between. The axial bearing may be fixed in the center bearing housing. An oil-deflecting plate may also be present to prevent the oil from entering the shaft sealing area.
Because the generated friction of a tapered-land bearing is sensitive to geometry, load, speed, and lubricant, such tapered-land bearing of a single/fixed geometry can be designed to meet a narrow operating range. For vehicle turbochargers, thrust bearings have been stamped or machined from one piece yielding a single geometry. Vehicle turbochargers experience a much larger operating range than most turbomachinery. Thus, an adaptive variable geometry thrust bearing is beneficial by offering optimal performance over a large operating range. It is desirable therefore to provide a turbocharger with an improved tapered-land thrust bearing assembly.